This invention relates to a process of producing an inorganic sulfur containing fluorine compound and more particularly pentafluorosulfur bromide (BrSF5).
BrSF5 is useful as a source of the pentafluorosulfur group (SF5) for introduction into organic compounds. The introduction of the SF5 group into organic molecules can significantly modify their physical, chemical, and biological properties. These modifications are useful in a variety of applications for products such as biologically active compounds, pharmaceuticals, perfluorinated blood substitutes, surface-active agents, agrochemicals and solvents for polymers. Further, BrSF5 can be used as an oxidizing agent.
BrSF5 can be produced by a variety of methods. For example, U.S. Pat. No. 3,338,685 to Merrill describes a process for producing BrSF5 comprising contacting a reaction mixture of SF4, Br2, and bromine pentafluoride (BrF5) in a sealed reactor at a temperature of about 50° C. to about 180° C. to obtain a 39% isolated yield of BrSF5 based on the amount of BrF5.
Other investigators have produced BrSF5 by heating a large excess of Br2 with S2F10 at 138°-150° C. for 16-24 hours. The observed yield of BrSF5 was 77-85% based on the amount of S2F10 consumed. See Cohen et al., Inorg. Chem. 4 (12): 1782-1785; (1965); Kovacina et al., J. Fluorine. Chem. 7:430-432 (1976); and Rahbarnoohi et al., Inorg. Chem. 22: 840-841 (1983).
Subsequently, others have obtained low to moderate yields of BrSF5 by reacting bromine fluoride (BrF) with sulfur tetrafluoride (SF4), in the presence of catalytic CsF. See Christe et al., Spectrochimica Acta. 33A (1977): 69-73; Winter et al., J. Fluorine Chem. 89 (1998): 105-106, and Seppelt et al., Chem. Ber. 116 (1983): 2399-2407).
Winter et al. reported a nearly quantitative (88.2-99.6% yield) synthesis of BrSF5 involving a six-week, room temperature, multi-step process of reacting BrF3 and Br2 with SF4 in the presence of catalytic CsF. In the first step or a preliminary reaction period of the synthesis of BrSF5, which lasted for 6 to 11 days at room temperature BrF3 and Br2 were reacted in the presence of catalytic CsF to form BrF. The second step or a reaction period involved reacting BrF with SF4 and lasted 36 days at room temperature or 20 days at elevated temperatures.
Similarly, Seppelt et al. described a synthesis of BrSF5, referencing Christe et al. (1977), as a two-step process wherein the first step of making BrF took 14 days at room temperature. The second step was performed at 90° C. for 15 hours and yielded 36% of BrSF5 based on the amount of SF4 consumed.
Steunenberg et al. J. Am. Chem. Soc. 79 (1957): 1320-1323 demonstrated that BrF3 and Br2 are in a temperature-dependent equilibrium with BrF.
These syntheses are not attractive candidates for industrial or even pilot-scale production of BrSF5 since they require successive steps, entail long reaction times, provide incomplete conversion of limiting reactants, or form large amounts of SF6 as a byproduct.
Accordingly, it is desired to provide an improved, scalable synthesis of BrSF5. It is further desired to prepare BrSF5 at high yields with relatively short reaction times. The increasing interest in SF5 containing chemicals and the limited availability of BrSF5 provided the motivation to develop an improved process for synthesis of BrSF5.
All references cited herein are incorporated herein by reference in their entireties.